Fuel additive mixtures for gasolines with synergistic ivd performance

ABSTRACT

Novel fuels for gasoline engines comprise a synergistic mixture of a detergent additive component (A) and a synthetic carrier oil component (B), i) the detergent additive component (A) comprising at least one compound having a basic nitrogen atom which is substituted by a hydrocarbyl radical having a number average molecular weight of from about 500 to 1 300, and the detergent additive component (A) being contained in the fuel in an amount of from about 30 to 180 ppm by weight; and ii) the carrier oil component (B) comprising at least one compound of the following formula I 
 
R—O—(A—O)x—H  (I)
where 
         R is a straight-chain or branched C 6 -C 18 -alkyl group;    A is a C 3 - or C 4 -alkylene group; and x is an integer from 5 to 35; the carrier oil component (B) being contained in the fuel in an amount of from about 10 to 180 ppm by weight.

The present invention relates to synergistic gasoline fuel additivecompositions having a synergistic performance in keeping the intakesystem clean, and gasoline engine fuels to which said compositions havebeen added.

Carburetors and intake systems of gasoline engines, but also injectionsystems for fuel metering, are increasingly being contaminated byimpurities which are caused by dust particles from the air, uncombustedhydrocarbon residues from the combustion chamber and the crank case ventgases passed into the carburetor.

These residues shift the air/fuel ratio during idling and in the lowerpart-load range so that the mixture becomes leaner, the combustionbecomes more incomplete and in turn the proportions uncombusted orpartially combusted by hydrocarbons in the exhaust gas become larger andthe gasoline consumption increases.

It is known that fuel additives for keeping valves and carburetors orinjection systems of gasoline engines clean are used for avoiding thesedisadvantages (cf. for example: M. Rossenbeck in Katalysatoren, Tenside,Mineralöladditive, edited by J. Falbe and U. Hasserodt, page 223, G.Thieme Verlag, Stuttgart 1978).

Depending on the mode of action, but also on the preferred site ofaction, of such detergent additives, a distinction is now made betweentwo generations.

The first additive generation was able only to prevent the formation ofdeposits in the intake system but not to remove existing deposits,whereas the modern additives of the second generation can do both(keep-clean and clean-up effect) and, owing to their excellent heatstability, can also do so in particular in zones of high temperature,i.e. in the intake valves. Such detergents, which can originate from alarge number of classes of chemical substances, for examplepolyalkeneamines, polyetheramines, polybutene Mannich bases orpolybutenesuccinimides, are used in general in combination with carrieroils and in some cases further additive components, for examplecorrosion inhibitors and demulsifiers. The carrier oils perform asolvent and wash function in combination with the detergents. Carrieroils are, as a rule, high-boiling, viscous, thermally stable liquidswhich coat the hot melt surface and thus prevent the formation ordeposition of impurities on the metal surface.

Such formulations of detergents with carrier oils can in principle bespecified as follows (depending on the type of the carrier oil orcarrier oils:

-   -   a) mineral oil-based (i.e. only mineral oil-based (mineral)        carrier oils are used),    -   b) completely synthetic (i.e. only synthetic carrier oils are        used) or, used in minor amounts,    -   c) semisynthetic (i.e. mixtures of mineral oil-based and        synthetic carrier oils are used).

It is known from the prior art that the additive formulations describedare used in gasoline fuels. It is generally considered that completelysynthetic additive packets have somewhat better keep-clean propertiesthan mineral oil-based ones.

EP-A-0 704 519 describes additive mixtures for fuels, comprising atleast one amine with a hydrocarbon radical having an average molecularweight of from 500 to 10 000, at least one hydrocarbon polymer having anaverage molecular weight of from 300 to 10 000 in hydrogenated orunhydrogenated form and, as a carrier oil component, a mixture ofpolyethers based on propylene oxide and/or butylene oxide and esters ofmono- or polycarboxylic acids and alkanols or polyols. In a comparativeexample disclosed therein, polyisobutenamine (molecular weight about 1000) and an isotridecanol, reacted with 22 mol of butylene oxide, areadded in amounts of, in each case, 300 ppm to gasoline fuel. There is noreference in this document to a possible synergistic reaction betweencarrier oil and detergent additive.

EP-A-0 548 617 describes gasoline fuels to which an additive combinationcomprising from 10 to 5 000 ppm of a nitrogen-containing detergentadditive and from 10 to 5 000 ppm of a phenol-initiated propoxylate havebeen added. In an individual comparative example, a mixture ofpolyisobutylamine and an alcohol butoxylate not defined in more detailis described. In each case 200 ppm of these two components are added toa fuel. There is no reference to a possible synergistic interactionbetween these two components in the stated amounts.

EP-A-0 374 461, corresponding to U.S. Pat. No. 5,004,478, describesgasoline fuels to which has been added a mixture of from 50 to 1 000 ppmof nitrogen-containing detergent additive and from 50 to 5 000 ppm of acarrier oil mixture of a) a polyalkylene oxide based on propylene oxideand/or butylene oxide and having a molar mass of at least 500, which wasprepared with aliphatic or aromatic mono-, di- or polyalcohols, aminesor amides or with alkylphenols as an initiator molecule, and b) estersof monocarboxylic acids or polycarboxylic acids and alkanols or polyols,these esters having a minimum viscosity of 2 cm²/s at 100° C. Onceagain, no reference is made to a synergistic interaction betweendetergent additive and polyether component in this publication.

EP-A-0 706 553 describes fuel additive compositions comprising ahydrocarbon-substituted amine having a molecular weight of from about700 to 2 000, a polyolefin polymer of a C₂-C₆-monoolefin having amolecular weight of from about 350 to 2 000 and apoly(oxyalkylene)monool having a terminal hydrocarbon group and anaverage molecular weight of from about 500 to 5 000, the terminalhydrocarbon group being a C₁-C₃₀-hydrocarbyl group. Specific examples ofsuch polyether components are dodecylphenol-initiated poly(oxy)butyleneshaving a molecular weight of about 1 500 which are preferably used incombination with a polyisobutenamine having a molecular weight of 1 300.Alkanol-initiated polyether compounds and their combined use withdetergent additives are not described in this publication.

EP-A-0 887 400 describes gasoline fuel mixtures to which from 50 to 70ppm of N-containing detergent having a molecular weight of from 700 to 3000 and from 35 to 75 ppm of hydrocarbyl-terminatedpoly(oxyalkylene)monool having a molecular weight of from 500 to 5 000have been added. Preferred hydrocarbyl terminal groups areC₇-C₃₀-alkylphenyl groups, in particular dodecylphenyl.

However, the additive packets known to date require furtheroptimization.

It is an object of the present invention to provide, for gasoline fuels,fuel additive packets which have very good keep-clean effects in theintake system.

We have found that this object is achieved and that, according to theinvention, formulations for gasoline fuels can be provided by the choiceof defined mixtures of synthetic carrier oils and detergent additives,which formulations cooperate synergistically in a particularlyadvantageous manner and are particularly effective in cleaning theintake system.

The present invention firstly relates to fuels for gasoline engines,comprising a synergistic mixture of a detergent additive component (A)and a synergistic carrier oil component (B),

-   -   i) the detergent additive component (A) comprising at least one        compound having a basic nitrogen atom which is substituted by a        hydrocarbyl radical having a number average molecular weight of        from about 500 to 1 300, and the detergent additive        component (A) being present in the fuel in an amount of from        about 30 to 180 ppm by weight, and    -   ii) the carrier oil component (B) comprising at least one        compound of the following formula I        R—O—(A—O)x—H  (I)        where    -   R is a straight-chain or branched C₆-C₁₈-alkyl group,    -   A is a C₃- or C₄-alkylene group and    -   x is an integer from 5 to 35,        the carrier oil component (B) being present in the fuel in an        amount of from about 10 to 180 ppm by weight.

Fuels comprising component (A) in an amount of from 50 to 150, inparticular from 70 to 130, ppm by weight and fuels comprising component(B) in an amount of from 20 to 150, in particular from 50 to 130, ppm byweight are preferably provided.

According to a further preferred variant, the novel fuels comprise apolyisobutenamine as component (A). Preferably, component (B) is acompound of the formula I, where R is a straight-chain or branchedC₈-C₁₅-alkyl group, A is butylene and/or x is an integer from 16 to 25,in particular from 20 to 24. An isotridecanol butoxylate is particularlypreferably used as component (B).

The present invention furthermore relates to the use of a synergisticadditive combination according to the above definition as gasoline fueladditive for cleaning the engine intake system.

A detailed description of the invention follows.

1. Detergent Additive Component (A)

Fuel additive compositions preferred according to the inventioncomprise, as a detergent additive component (component A), a detergentadditive selected from polyalkenemonoamines and polyalkenepolyamines andmixtures thereof. Examples of polyalkenamines which may be used arepoly-C₂-C₆-alkenamines and functional derivatives thereof, which in eachcase contain a hydrocarbyl radical having a preferred Mn of from about500 to 1 500, preferably from about 600 to 1 200, in particular fromabout 700 to 1 100, g. In addition to ammonia, suitable amines includemono- and di-C₁-C₆-alkylamines, such as mono- and dimethylamine, mono-and diethylamine, mono- and di-n-propylamine, mono- and di-n-butylamine,mono- and di-sec-butylamine, mono- and di-n-pentylamine, mono- anddi-2-pentylamine, mono- and di-n-hexylamine, etc. Further suitableamines are diamines, such as ethylenediamine, propylene 1,2-diamine,propylene 1,3-diamine, butylenediamines and the mono-, di- and trialkylderivatives of these amines. It is also possible to use, as polyamines,polyalkylenepolyamines which have up to 6 nitrogen atoms and whosealkylene radicals are of 2 to 6 carbon atoms, such asdiethylenetriamine, triethylenetetramine and tetraethylenepentamine.Also suitable are mono- or dialkylamines in which the alkyl radicals maybe interrupted by one or more nonneighboring oxygen atoms and which mayalso have hydroxyl groups. These include, for example, ethanolamine,3-aminopropanol, 2-(2-aminoethoxy)ethanol andN-(2-aminoethyl)ethanolamine.

Polyalkenemonoamines or polyalkenepolyamines which can be used inparticular according to the invention or functional derivatives thereofare in particular poly-C₂-C₆-alkenamines, such as poly-C₃- orC₄-alkenamines, or functional derivatives thereof, e.g. compounds havinga hydrocarbyl radical, prepared by polymerization of ethylene, propene,1- or 2-butene, isobutene or mixtures thereof.

Examples of functional derivatives of the above additives are compoundswhich carry one or more polar substituents, in particular hydroxylgroups, for example in the amine moiety.

Preferred additives which can be used according to the invention arepolyalkenemonoamines or polyalkenepolyamines based on polypropene or onhighly reactive (i.e. having predominantly terminal double bonds) orconventional (i.e. having predominantly internal double bonds)polybutene or polyisobutene.

Particularly suitable polyisobutenes are highly reactive polyisobuteneswhich have a high content of terminal ethylenic double bonds. Suitablehighly reactive polyisobutenes are, for example, polyisobutenes whichcontain more than 70, in particular more than 80, especially more than85, mol % of vinylidene double bonds. Polyisobutenes which have uniformpolymer skeletons are particularly preferred. Uniform polymer skeletonsare possessed in particular by those polyisobutenes which are composedof at least 85, preferably at least 90, particularly preferably at least95, % by weight of isobutene units. Such highly reactive polyisobutenespreferably have a number average molecular weight M_(N) in theabovementioned range. In addition, the highly reactive polyisobutenesmay have a polydispersity of less than 1.9, e.g. less than 1.5.Polydispersity is understood as meaning the quotient of weight averagemolecular weight M_(W) and number average molecular weight M_(N).

Such additives based on highly reactive polyisobutene which can beprepared from polyisobutene which may contain up to 20% by weight ofn-butene units by hydroformylation and reductive amination with ammonia,monoamines or polyamines, such as dimethylaminopropylamine,ethylenediamine, diethylenetriamine, triethylenetetramine andtetraethylenepentamine, are disclosed in particular in EP-A-0 244 616 orEP-A-0 578 323.

If polybutene or polyisobutene having predominantly internal doublebonds (generally in the beta- and gamma-positions) is used as thestarting material in the preparation of the additives, the preparationby chlorination and subsequent amination or by oxidation of the doublebond with air or ozone to give the carbonyl or carboxyl compound andsubsequent amination under reductive (hydrogenating) conditions ispossible. Here, the amines used for the amination may be the same asthose used above for the reductive amination of the hydroformylatedhighly reactive polyisobutene. Corresponding additives based onpolypropene are described in particular in WO-A-94/24231.

Further preferred monoamino-containing additives are the compoundsobtainable from polyisobutene epoxides by reaction with amines andsubsequent dehydration and reduction of the amino alcohols, as describedin particular in DE-A 196 20 262.

Detergent additives of the polyalkeneamine type which may be used inparticular are sold by BASF AG, Ludwigshafen, under the trade nameKerocom PIBA. These contain polyisobutenamines dissolved in aliphaticC₁₀-C₁₄-hydrocarbons and can be used as such in the novel additivepackets.

The fuel additive mixtures used according to the invention can, ifrequired, contain further gasoline fuel additives differing from (A) andhaving a detergent effect or an effect which inhibits valve seat wear(referred to below as detergent additives). These detergent additiveshave at least one hydrophobic hydrocarbon radical having a numberaverage molecular weight (M_(N)) of from 85 to 20 000 and at least onepolar group selected from:

-   -   (a) mono- or polyamino groups having up to 6 nitrogen atoms, at        least one nitrogen atom having basic properties;    -   (b) nitro groups, if required in combination with hydroxyl        groups;    -   (c) hydroxyl groups in combination with mono- or polyamino        groups, at least one nitrogen atom having basic properties;    -   (d) carboxyl groups or the alkali metal or alkaline earth metal        salts thereof;    -   (e) sulfo groups or the alkali metal or alkaline earth metal        salts thereof;    -   (f) polyoxy-C₂- to C₄-alkylene groups which are terminated by        hydroxyl groups or mono- or polyamino groups, at least one        nitrogen atom having basic properties, or by carbamate groups;    -   (g) carboxylic ester groups;    -   (h) groups derived from succinic anhydride and having hydroxyl        and/or amino and/or amido and/or imido groups; and    -   (i) groups produced by Mannich reaction of substituted phenols        with aldehydes and mono- or polyamines.

The hydrophobic hydrocarbon radical in the above detergent additiveswhich ensures sufficient solubility in the fuel has a number averagemolecular weight (M_(N)) of from 85 to 20 000, in particular from 113 to10 000, especially from 300 to 5 000. A typical hydrophobic hydrocarbonradical, in particular in combination with the polar groups (a), (c),(h) and (i), is the polypropenyl, polybutenyl or polyisobutenyl radical,having in each case an M_(N) of from 300 to 5 000, in particular from500 to 2 500, especially from 700 to 2 300.

The following are examples of the above groups of detergent additives:

Additives containing mono- or polyamino groups (a) are preferablypolyalkenemonoamines or polyalkenepolyamines based on polypropene or onhighly reactive (i.e. having predominantly terminal double bonds) orconventional (i.e. having predominantly internal double bonds)polybutene or polyisobutene having an M_(N) of from 300 to 5 000. Suchadditives based on highly reactive polyisobutene, which can be producedfrom the polyisobutene, which may contain up to 20% by weight ofn-butene units, by hydroformylation and reductive amination withammonia, monoamines or polyamines, such as dimethylaminopropylamine,diethylenediamine, diethylenetriamine, triethylenetetramine ortetraethylenepentamine, are disclosed in particular in EP-A-244 616. Ifpolybutene or polyisobutene having predominantly internal double bonds(generally in the beta- and gamma-positions) are used as a startingmaterial in the preparation of the additives, the preparation bychlorination and subsequent amination or by oxidation of the double bondwith air or ozone to give the carbonyl or carboxyl compound andsubsequent amination under reductive (hydrogenating) conditions ispossible. The amines which can be used here for the amination are thesame as those used above for the reductive amination of thehydroformylated highly reactive polyisobutene. Corresponding additivesbased on polypropene are described in particular in WO-A-94/24231.

Further preferred additives containing monoamino groups (a) are thehydrogenation products of the reaction products of polyisobutenes havingan average degree of polymerization P of from 5 to 100 with oxides ofnitrogen or mixtures of oxides of nitrogen and oxygen, as described inparticular in WO-A-97/03946.

Further preferred additives containing monoamino groups (a) are thecompounds obtainable from polyisobutene epoxides by reaction with aminesand subsequent dehydration and reduction of the amino alcohols, asdescribed in particular in DE-A-196 20 262.

Additives containing nitro groups, if required in combination withhydroxyl groups, (b) are preferably reaction products of polyisobuteneshaving an average degree of polymerization P of from 5 to 100 or from 10to 100 with oxides of nitrogen or mixtures of oxides of nitrogen andoxygen, as described in particular in WO-A-96/03367 and WO-A-96/03479.These reaction products are as a rule mixtures of purenitropolyisobutanes (e.g. α,β-dinitropolyisobutane) and mixedhydroxynitropolyisobutanes (e.g. α-nitro-β-hydroxypolyisobutane).

Additives containing hydroxyl groups in combination with mono- orpolyamino groups (c) are in particular reaction products ofpolyisobutene epoxides, obtainable from polyisobutene having preferablypredominantly terminal double bonds and having an M_(N) of from 300 to 5000, with ammonia or mono- or polyamines, as described in particular inEP-A-476 485.

Additives containing carboxyl groups or the alkali metal or alkalineearth metal salts thereof (d) are preferably copolymers ofC₂-C₄₀-olefins with maleic anhydride, having a total molar mass of from500 to 20 000, some or all of whose carboxyl groups have been convertedinto the alkali metal or alkaline earth metal salts and a remainder ofwhose carboxyl groups have been reacted as alcohols or amines. Suchadditives are disclosed in particular in EP-A-307 815. Additives of thistype serve mainly for preventing valve seat wear and, as described inWO-A-87/01126, can advantageously be used in combination withconventional fuel detergents, such as poly(iso)butenamines orpolyetheramines.

Additives containing sulfo groups or the alkali metal or alkaline earthmetal salts thereof (e) are preferably alkali metal or alkaline earthmetal salts of an alkyl sulfosuccinate, as described in particular inEP-A-639 632. Additives of this type serve mainly for preventing valveseat wear and can advantageously be used in combination withconventional fuel detergents, such as poly(iso)butenamines orpolyetheramines.

Additives containing polyoxy-C₂-C₄-alkylene groups (f) are preferablypolyether or polyetheramines which are etheramines which are obtainableby reacting C₂-C₆₀-alkanols, C₆-C₃₀-alkanediols, mono- ordi-C₂-C₃₀-alkylamines, C₁-C₃₀-alkylcyclohexanols or C₁-C₃₀-alkylphenolswith from 1 to 30 mol of ethylene oxide and/or propylene oxide and/orbutylene oxide per hydroxyl group or amino group and, in the case of thepolyetheramines, by subsequent reductive amination with ammonia,monoamines or polyamines. Products of this type are described inparticular in EP-A-310 875, EP-A-356 725, EP-A-700 985 and U.S. Pat. No.4 877 416. In the case of polyethers, such products also have carrieroil properties. Typical examples thereof are tridecanol butoxylates andisotridecanol butoxylates, isononylphenol butoxylates and polyisobutenolbutoxylates and propoxylates and the corresponding reaction productswith ammonia.

Additives containing carboxylic ester groups (g) are preferably estersof mono-, di- or tricarboxylic acids with long-chain alkanols orpolyols, in particular those having a minimum viscosity of 2 mm²/s at100° C., as described in particular in DE-A-38 38 918. Mono-, di- ortricarboxylic acids which may be used are aliphatic or aromatic acids,and particularly suitable ester alcohols or ester polyols are long-chainmembers of, for example, 6 to 24 carbon atoms. Typical members of theesters are adipates, phthalates, isophthalates, terephthalates andtrimellitates of isooctanol, of isononanol, of isodecanol and ofisotridecanol. Such products also have carrier oil properties.

Additives which contain groups derived from succinic anhydride andhaving hydroxyl and/or amino and/or amido and/or imido groups (h) arepreferably corresponding derivatives of polyisobutenylsuccinicanhydride, which are obtainable by reacting conventional or highlyreactive polyisobutene having an M_(N) of from 300 to 5 000 with maleicanhydride by a thermal method or via the chlorinated polyisobutene. Ofparticular interest here are derivatives with aliphatic polyamines, suchas ethylenediamine, diethylenetriamine, triethylenetetramine ortetraethylenepentamine. Such gasoline fuel additives are described inparticular in U.S. Pat. No. 4 849 572.

Additives containing groups (i) produced by Mannich reaction ofsubstituted phenols with aldehydes and mono- or polyamines arepreferably reaction products of polyisobutenyl-substituted phenols withformaldehyde and mono- or polyamines, such as ethylenediamine,diethylenetriamine, triethylenetetramine, tetraethylenepentamine ordimethylaminopropylamine. The polyisobutenyl-substituted phenols mayoriginate from conventional or highly reactive polyisobutene having anM_(N) of from 300 to 5 000. Such polyisobutene Mannich bases aredescribed in particular in EP-A-831 141.

For a more exact definition of the individual gasoline fuel additivesmentioned, reference is made here expressly to the disclosures of theabovementioned publications of the prior art.

2. Carrier Oil Component (B)

The novel carrier oil component (B) comprises at least one compound ofthe following formula IR—O—(A—O)x—H  (I)where

-   -   R is a straight-chain or branched C₆-C₁₈-alkyl, in particular        C₈-C₁₅-alkyl, group,    -   A is a C₃- or C₄-alkylene group and    -   x is an integer from 5 to 35, e.g. from 16 to 25 or from 20 to        24.

Examples of suitable radicals R are n-hexyl, n-heptyl, n-octyl, n-nonyl,n-decyl, n-undecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyland n-octadecyl and the singly or multiply branched analogs thereof,such as isotridecyl, and mixtures of such isomers.

Examples of suitable radicals A are propylene, 1- and 2-butylene andisobutylene.

Examples of suitable polyethers (B) are preferably compounds whichcontain polyoxy-C₂-C₄-alkylene groups and are obtainable by reactingC₆-C₁₈-alkanols with from 5 to 35 mol of a C₃-C₄-alkylene oxide perhydroxyl group. Such products are described in particular in EP-A-0 310875, EP-A-0 356 725, EP-A-0 700 985 and U.S. Pat. No. 4,877,416. Typicalexamples of these are tridecanol butoxylates or isotridecanolbutoxylates and corresponding isomer mixtures thereof.

3. Further Additives

Further conventional additives for the novel fuels are corrosioninhibitors, for example based on ammonia salts of organic carboxylicacids, which salts tend to form films, or on heterocyclic aromatics inthe case of inhibition of corrosion of nonferrous metals; antioxidantsor stabilizers, for example based on amines, such as p-phenylenediamine,dicyclohexylamine or derivatives thereof, or on phenols, such as2,4-tert-butylphenol or 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid;demulsifiers; antistatic agents; metallocenes, such as ferrocene;methylcyclopentadienylmanganesetricarbonyl; lubricity additives, such ascertain fatty acids, alkenylsuccinic esters, bis(hydroxyalkyl) fattyamines, hydroxyacetamides or castor oil; and markers. If required,amines may also be added for reducing the pH of the fuel.

The components or additives can be added to the gasoline fuelindividually or as a previously prepared concentrate (additive packet),together with the novel high molecular weight polyalkene.

Said detergent additives differing from (A) and having polar groups (a)to (i) are added to the gasoline fuel usually in an amount of from 10 to5 000, in particular from 50 to 1 000, ppm by weight. The othercomponents and additives mentioned are, if desired, added in amountscustomary for this purpose.

4. Gasoline Fuels

The novel additive compositions can be used in all conventional gasolinefuels, as described, for example, in Ullmann's Encyclopedia ofIndustrial Chemistry , 5th edition, 1990, Volume A16, page 719 et seq.

For example, use in a gasoline fuel having an aromatics content of notmore than 42% by volume and a sulfur content of not more than 150 ppm byweight is possible.

The aromatics content of the gasoline fuel is, for example, from to 42,preferably from 32 to 40, % by volume.

The sulfur content of the gasoline fuel is, for example, from 5 to 150,in particular from 10 to 100, ppm by weight.

The gasoline fuel has, for example, an olefin content of from 6 to 21,in particular from 7 to 18, % by volume.

The gasoline fuel may have, for example, a benzene content of from 0.5to 1.0, in particular from 0.6 to 0.9, % by volume.

The gasoline fuel has, for example, an oxygen content of from 1.0 to2.7, in particular from 1.2 to 2.0, % by weight.

In particular, those gasoline fuels which simultaneously have anaromatics content of not more than 38% by volume, an olefin content ofnot more than 21% by volume, a sulfur content of not more than 50 ppm byweight, a benzene content of not more than 1.0% by volume and an oxygencontent of from 1.0 to 2.7% by weight may be mentioned by way ofexample.

The content of alcohols and ethers in the gasoline fuel is usuallyrelatively low. Typical maximum contents are 3% by volume for methanol,5% by volume for ethanol, 10% by volume for isopropanol, 7% by volumefor tert-butanol, 10% by volume for isobutanol and 15% by volume forethers having 5 or more carbon atoms in the molecule.

The summer vapor pressure of the gasoline fuel is usually not more than70, in particular 60, kPa (in each case at 37° C.).

The RON of the gasoline fuel is as a rule from 90 to 100. A conventionalrange for the corresponding MON is from 80 to 90.

The stated specifications are determined by conventional methods (DIN EN228).

The examples which follow illustrate the invention.

EXAMPLE

A mixture of equal parts of the detergent additive(PIBA=polyisobutenemonoamine (M_(W)=1 000)) and isotridecanol,etherified with 22 mol of butylene oxide, is prepared and is added to acommercial base fuel according to DIN EN 228 in different amounts. Forcomparison, only PIBA is added to the same fuel.

With these fuels and with additive-free fuel, a Mercedes Benz M 102engine test is carried out for determining the intake system deposits(CEC F-05-A-93). The results are summarized in the table below.

The test results show that, in spite of a lower detergent additivecontent, the novel additive mixtures have a substantially bettercleaning effect in the intake system. TABLE 1 Test Dosage³⁾ Valvedeposit (mg/valve) Mean No. Additive mg/kg 1 2 3 4 value 1 —  0 293 593296 338 380 2 PIBA¹⁾ 200 42 11 108 99 65 3 PIBA¹⁾/ 100/100 5 25 100 5246 Polyether²⁾ 4 PIBA¹⁾/ 134/134 10 8 48 7 18 Polyether²⁾¹⁾PIBA = Polyisobutenamine (M_(W) = 1000)²⁾Polyether = Isotridecanol, etherified with 22 1-butylene oxide units³⁾Dosage based in each case on pure substance

1. A fuel for gasoline engines, comprising a synergistic mixture of adetergent additive component (A) and a synthetic carrier oil component(B), i) the detergent additive component (A) comprising at least onecompound having a basic nitrogen atom which is substituted by ahydrocarbyl radical having a number average molecular weight of fromabout 500 to 1 300, the detergent additive component (A) being presentin the fuel in an amount of from about 30 to 180 ppm by weight, and ii)the carrier oil component (B) comprising at least one compound of thefollowing formula IR—O—(A—O)x—H  (I) where R is a straight-chain or branched C₆-C₁₈-alkylgroup; A is a C₃- or C₄-alkylene group and x is an integer from 5 to 35,the carrier oil component (b) being present in the fuel in an amount offrom about 10 to 180 ppm by weight:
 2. A fuel as claimed in claim 1,comprising component (A) in an amount of from 50 to 150 ppm by weight.3. A fuel as claimed in either of the preceding claims, comprisingcomponent (A) in an amount of from 70 to 130 ppm by weight.
 4. A fuel asclaimed in any of the preceding claims, comprising component (B) in anamount of from 20 to 150 ppm by weight.
 5. A fuel as claimed in any ofthe preceding claims, comprising component (B) in an amount of from 60to 130 ppm by weight.
 6. A fuel as claimed in any of the precedingclaims, component (A) being a polyisobutenamine.
 7. A fuel as claimed inany of the preceding claims, component (B) being a compound of theformula I, where R is a straight-chain or branched C₈-C₁₅-alkyl group.8. A fuel as claimed in any of the preceding claims, component (B) beinga compound of the formula I, where A is butylene.
 9. A fuel as claimedin any of the preceding claims, component (B) being a compound of theformula I, where x is an integer from 16 to
 25. 10. A fuel as claimed inany of the preceding claims, component (B) being a compound of theformula I, where x is an integer from 20 to
 24. 11. A fuel as claimed inany of the preceding claims, component (B) being a tridecanolbutoxylate.
 12. A synergistic fuel additive mixture according to thedefinition in any of the preceding claims.
 13. The use of a synergisticadditive combination as claimed in claim 12 as a gasoline fuel additivefor cleaning the engine intake system.